Converting G1214M Cone 6 transparent glaze to G1214Z matte

How I converted a glossy glaze into a matte glaze by using glaze chemistry and recipe logic.

A. Insight-live

Transcript/Notes

Scene 1
To demonstrate the utility of viewing a glaze as a formula rather than a recipe - Let’s convert a glossy cone 6 glaze into a matte.
I’ll use the “Advanced Search”, choose the “demonstration recipes”, look for “G1214”, and open the M version.
Then, I will duplicate it, edit it, auto-assign a new code number (for writing on test specimens), and change the name to “Cone 6 Calcium Matte”.
Then, I’ll turn on “formula calculation” for it.

more..

Finally, from the “Limit Recipes”, I’ll clear the search field and choose the TARGET2.
Notice the maximum Al₂O₃ is 0.65 and the minimum SiO₂ is 2.4.
We are going to be crowding both of these limits to get a matte.

Scene 2
Notice also the recommended maximum for calcium oxide: 0.55.
And the note “CaO can be higher if MgO is zero”.
But the clear glaze has 0.79. Why? It was formulated to work with chrome-tin stains, they require high calcium oxide.
This makes it an ideal starting point to make a calcium matte.
Our glaze also needs lower silicon dioxide and higher alumina oxide.
Their current ratio is 9.4:1. But for a matte we need around 5:1 (I can click here to find out more).
The first step is to reduce the silica.
To do that I’ll click here,, set the increment at “20” and click the silica down arrow.
That reduces the Silica:Alumina ratio considerably.
Step two is to increase alumina oxide. Notice how high the alumina content of kaolin is.
I’ll double its amount in the recipe.
Now the ratio is way down.
Notice how aggressive I had to be to effect the desired changes in the chemistry.

Scene 3 (start here)
Now I have a problem: This calculated thermal expansion is too high to fit the clay bodies I use.
That’s because of the combination of these two.
If I click on the sodium we can see its thermal expansion: 0.387 (by the way, this works because of the tight integration between Insight-live and the Digitalfire Reference Library).
And potassium is almost as much.
But notice calcium oxide: 0.148. Much lower.
My plan is to increase it at the expense of the sodium and potassium, increasing the matteness and reducing the thermal expansion at the same time.
The Feldspar is the main contributor of KNaO (the combination of the two).
Let’s display it beside Ferro frit 3124.
The Frit 3124 has all the things I want:
-Less KNaO than the feldspar
-More CaO than the feldspar
-Significent Al₂O₃ and enough B₂O₃ to melt the glaze well
The existing 3134 only has two of these benefits.

Scene 4:
Now I’ll make three changes:
-Change the kaolin amount back to 20.
-Zero the 3134
-Replace the feldspar with Frit 3124
Notice the impact on the calculated formula: The B203 is down.
You may remember that its concentration is lower in 3124 than in 3134.
So, I’ll use the Frit 3124 increment arrow (set at “1”) to get it back up to 0.2.
-Then I’ll use the kaolin increment arrow to increase the Al₂O₃ to 0.45.
-Finally, I’ll do the same with the silica to take the SiO₂ to 2.5.
Notice I have achieved my goal in the formula.
-There is more CaO and less KNaO.
-The thermal expansion is significantly down.
-The silica and alumina are about where I want them.

Scene 5:
There is another possible problem here: Too much kaolin (26 out of 77), this creates the danger that the glaze may shrink, crack and then crawl on firing.
To fix that I’ll replace ⅓ of the raw kaolin with calcined kaolin.
I’ll just borrow the unused Frit 3134 line for it and use values of 17 and 9.
This pushes up the Al₂O₃. That happens because the calcined material is more concentrated.
I’ll nudge the raw kaolin one down to rematch the Al₂O₃ in the formula.

Scene 6:
Matte glazes look best when they have opacity.
I’ll add four parts Zircopax (by editing with more columns).
I’ll set it not to participate in the calculated chemistry using this checkbox. Then Save.
Finally, I’ll re-total to 104 (100 for the recipe plus 4 for opacifier)
I’ll check this box so the Zircopax stays at 4.
Normally I would finish by rounding off each amount to the nearest tenth.
Let replace the feldspar panel with Frit 3124.
We have the glossy original, new matte and the material that made this possible
The CaO is higher at the expense of sodium and potassium oxide.
And the Si:Al ratio is less than half.
The thermal expansion is the same.
And we have some nice adjustability in the ratio of raw to calcined clay.

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You will see examples of replacing unavailable materials (especially frits), fixing various issues (e.g. running, crazing, settling), making them melt more, adjusting matteness, etc. Insight-Live has an extensive help system (the round blue icon on the left) that also deals with fixing real-world problems and understanding glazes and clay bodies.

I converted a glossy transparent glaze to a calcium matte

Glaze chemistry and recipe logic were the enablers

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This is beyond interesting if you want to know more about glazes, recipes and their chemistry. This is simple and easy for anyone to understand. Watch me adjust the recipe of my high-calcium transparent cone 6 glaze to convert it to a calcium matte. I'll do it in my Insight-live.com. We'll cut the Si:Al ratio, increase the CaO further, maintain the thermal expansion for glaze fit and make the recipe shrinkage-adjustable using a mix of calcined and raw kaolin.

By Tony Hansen
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